A distributed security system may include multiple processing units that perform different functions. For example, the distributed security system may include multiple security processing units (SPUs) that manage sessions for a packet flow, apply security features to a packet, and apply packet-based stateless firewall filters, classifiers, and traffic shapers to the packet. In some implementations, the distributed security system may use a processor as a central point to manage arbitration and allocation of resources and distribute sessions. This architecture allows processing of sessions to be distributed across multiple SPUs.